The present invention is concerned with fibre drum construction, and more particularly relates to a large capacity integrally-lined fibre drums, for example 55 gallon, 21.5 inch diameter drums approximately 37 to 38 inches tall, wherein drum breakage or rupture from accidental dropping or similar abuse is a substantial problem limiting utilization of the drums.
Integrally-lined fibre drums have been used for many years for packaging and shipping of dry goods and, to some degree, nonhazardous liquids. Such drums have not been used with hazardous liquids due to concern about their ability to withstand the abuse to which the drums may be subjected during handling and shipping. To qualify for such use, the drum must pass various standards, for example as set forth in U.S. Department of Transportation (DOT) Regulations which include the requirement that a 55 gallon drum, filled with water to 98% capacity, must not leak when dropped from a four foot height onto a solid concrete surface so as to land diagonally on a corner chime, i.e., the junction of the top or bottom with the sidewall of the drum.
Steel drums, plastic drums and fibre drums with loose plastic inserts will normally pass the DOT "drop test". However, when commercially available, integrally-lined fibre drums are subjected to the four-foot diagonal drop test, they typically fail by one or more of the following:
(1) Catastrophic sidewall tearing;
(2) Pullout or tearout of the bottom heading from the steel chime band; and
(3) Limited extent tearing (fracture) of the sidewall adjacent to the steel chime band.
The typical fibre drum is an open-top paperboard barrel. Most often the drum bottom, called the bottom heading, and the tubular sidewall are made of paperboard. Top closures, called covers, are usually made of paperboard, sheet metal, or plastic. Wooden bottoms and covers are also used, but in only a small fraction of domestically produced drums.
Fibre drums can be assembled by a variety of processes including gluing, stapling, etc. By far the most widely used method of fibre drum construction employs steel chime bands at both the top and bottom of the drum. During manufacture, a relatively loose assembly consisting of a tubular sidewall, top and bottom chime bands, and bottom heading is converted into a sturdy unitary structure by a sequence of grooving, curling, and crimping operations performed simultaneously on the fibre and metal components.
At the bottom of the finished drum, the chime band, tube end portion, and bottom heading are formed together to define a closed bottom with a reinforced sealed annular periphery.
At the top of the finished drum, the chime band is curled over the end of the fibre tube to form a circumferential bead against which the cover can be separately sealed. The cover will normally be held in place by a C-shaped split steel locking band with a channel cross-section. The opening in the band is spanned by a toggle mechanism which pulls the open ends of the band toward each other after the band has been slipped over the cover and engaged with the recess or groove formed in the top chime and sidewall. The upper leg of the C-shaped band bears against the top of the cover near its perimeter, while the lower leg bears against the part of the chime band forming the upper surface of the top groove.
Alternatively, the finished drum can be a tight-head drum wherein a top heading is permanently mounted in a manner duplicating the mounting of the bottom heading. In such case, the top heading will include appropriate bung and vent fittings.
U.S. Pat. Nos. 2,696,340 and 2,727,673, issued respectively Dec. 7, 1954 and Dec. 20, 1955, to Bergstrom, illustrate conventional drum construction features.
Drum constructions often include special features. The inner plies of the tube, top heading and bottom heading of a drum for liquid contents may be made of plastic/paper laminates. Tubes for drums which must be able to withstand outdoor storage are wound with a waterproof adhesive. The inner surface of drums for certain chemical or food products may require special gas, i.e. oxygen, impermeable linings.
For many years the typical general purpose fibre drum has been constructed with steel chime bands for reinforcement and joint stability. While such reinforcement has sufficed for solid foodstuffs, granular material and the like, problems arise from the expansion of the use of fibre drums as containers for liquids. Improved resistance to damage from abusive handling, the chief cause of drum failure, has been found to be necessary if integrally lined liquid-tight fibre drums are to comprise a viable alternate to the heavier, more costly metal drums, plastic drums, or fibre drums with loose plastic inserts. In insuring product quality, assignee company routinely subjects its drums to industry standard tests, including the Department of Transportation (DOT) test which simulates the accidental dropping of a drum from a loading dock or truck body.
Fibre drums of appropriately conventional robust construction and containing an approved dry granulated test material can pass this test. However, integrally-lined fibre drums containing aqueous liquid contents have heretofore been unable to pass the test, i.e., to survive the 4-foot drop without leaking. In actuality, such drums have been seen to fail with drops as low as two feet.
Experimentation conducted with conventionally constructed fibre drums revealed the nature of the impact zone sidewall deformations and fractures. These tests indicated that the destructive deformation patterns resulted from unfavorable interactions between the chime skirt and sidewall at two locations in the impact region outwardly spaced to the opposite sides of the strike point. The chime bands of the test drums were relatively wide, extending about 1.3 inches below the horizontal surface of the chime groove. Long chime skirts increase stacking strength, a desirable characteristic in a drum intended to be able to withstand abusive service. The appearance of a failed drum at and near its fracture sites suggested that deformations might be less severe if the chime skirt did not extend down the sidewall from the groove. Subsequently, two drums with chime skirts of this kind were drop tested. Deformations were noted to be considerably less severe, but both drums continued to sustain small destructive fractures of the usual type. Thus, reduction of the chime skirt is not a viable solution in that this would both reduce the effectiveness of the chime for its intended purpose, and at the same time not preclude drum failure.
The present invention, resulting from not only a recognition of the problem but also a recognition as to the forces and conditions which produce the problem, uniquely avoids drum rupture or fracture in a simple and inexpensive manner which allows for use of conventional drum construction and materials.